We report a simple technique to synchronize solid etalons which provides identical sets of equally spaced absolute reference frequencies. To demonstrate the principle, we synchronized 1-mm thick fused silica etalons to have identical sets of resonant frequencies at 195.579 +/- n x 0.1034 THz, where n is any integer. These references were temperature-insensitive with the aid of a temperature control loop. These synchronized etalons could be used for standardizing the wavelengths of transmitter lasers in large scale WDM networks.